Downloaded from https://www.everyspec.com A. OVALITY F. ECCENTRICITY Figure 5-12, Ovality and eccentricity tolerances in general, the concentricity symbol should be of which the engineer must be aware. Figure used only when two or more surfaces are 5-15a shows the conditions which the engineer involved. When a single surface is involved, the desires, while figure 5-15b shows a condition desired conditions should not be stated interms which meets the requirement for parallelism, of concentricity, but of some other attribute, such but which may not be desired. as straightness.
cates that the surface or formutowhichthe sym- criminate between lack of parallelism and the The symbol for perpendicularity [ ] lndi- The normal inspection process will not dis- WIu Is at h.ue fse MtwUendiculaz to the condition shown in figure 5-15b. Rejection da...... ht suraeindiate by pern r tonte would be on the basis of nonconformance with datuib surae indicated by. one ex- ample is shown on page 8 of Drawing 30-1-7. the requirement expressed in figure 5-15a, Another example is illustrated here in figure whereas in fact the piece shown in figure 5-15a does meet the requirement. 5-13.
Figure 5-13a shows the intended conditions in In the case of a very light part exhibiting the a cone, that is, the entire form isperpendicular condition shown in figure 5-15b, the inspection to the base of the cone. Figure 5-13b shows process might accept the piece if the convex the condition which is to be controlled and the surface is resting on the surface plate, because method of checking. It should be noted that the the spring pressure of the dial indicator might cone in figure 5-13b is concentric but not per- cause the piece to roll in the direction that the pendicular. The condition shown cannot be con- indicator is moved. Consideration should be trolled by concentricity requirements.
given to a requirement for flatness of the datum However, concentricity requirements may be surface, in addition to the requirement for required in order to control the condition shown parallelism. in figure 5-14a. This cone is perpendicular to the base, but not concentric with the dijametral The symbol S indicates either synemetry or surface A. Figure 5-14b illustrates the correct centrality. Symmetry is the equal distribution toleancng o a lard coe tobtinthdesred of a form about a centerline. Centraliity is thr tolerancing of a flared cone toobtainthe desired spacing of surfaces equidistant trom a center- results. line.
In figure 13 of Drawing 30-1-7, thetongue Two examples of the use of the sy mbol for paral- at the bottom of the piece is symnietriicl about lelism i are given on page 9 of Drawing the centerline of the datum surfacet -7-7i•, The 30-1-7, the first of which requires parallelism slot at the top of the piece in equally -iistributed, between two surfaces, and the second of which that is, the sides of the slot are equidistant requires parallelism of a tapered form with a from the centerline of thedatum surface 1- 'P__) surface. However there are certain conditions ti actual practice, there are few occasions in 5-14